If you are having cranking issues with 1/0 it is not due to wire size, but rather something else, and there is lots of room
Wire end terminals.........wire terminals can be corroded or not making as great contact as you think
Switches. You are going through AT LEAST three switches to the starter........the disconnect, the Ford, and the original Mopar starter solenoid. Any one or two or all three could be introducing drop
The starter could have a problem
The ENGINE could have a problem
Have you done any "actual troubleshooting?" You know what a carbon pile tester is? Have you measured starter voltage and drop along the wiring in the system, and so on?
"Throwing parts" or "jacking up the radiator cap" is no way to fix anything, unless you simply like to spend money.
So!!!??? Do some checks. Get/ borrow a carbon pile tester. Get a multimeter and "rig" a long wire---which can be small, even no18---to reach to the far corners of the car, say 15-20ft long, with alligator clips each end.
Rig a remote starter to the starter relay
Check ground drop. You really should use TWO people. Clipe one probe of the meter to a good ground on the engine block. Stab the other probe into the top of the battery NEG teminal. Disable ignition so it will not fire. Crank the engine, read meter while cranking
Post the reading. You are hoping for a very low reading, the lower the better.
Now clip the meter to the starter side of the Ford solenoid. Stab the other into the top of the POS battery post. Crank and read. Same as above lower the better. You are hoping to see a FEW TENTHS of one volt
Now move up to the starter main terminal. Clip the meter there, and top on batter POS. Crank and read. Post reading.
Clip meter to starter main post and engine ground, crank and read. The higher the better Should have bare minimum 10V, acceptable is 10.5 or higher.
